Our company wish to play D&D on the base of your game, TableTop Simulator (everyone has a Steam version). But we faced a problem while preparations - our Game Master cannot connect to us. He appeares in the list of players while been in our session, but only we can see it - he cannot even choose his colour. Firstly, we thought that it was a problem on our side - everyone exept him is from Russia, he is from Israel. But even after following advices, presented on official Steam forum and here, we cannot decide our problem.
Would you help us to decide it?

P. S. He had played with some of us before with the same computer and Internet and everything was OK.